Never come in and try to change everything after a beloved teacher leaves!
Change one thing this year and indeed focus on fun. Be more demanding with your 6th graders since they didn't know the other guy. 7th graders make it clear to them that you like the old guy and the traditions. Change things without them noticing.
Placate the 8th graders or they will revolt against you.
Next year, you can pretty much teach how you want and you'll have only a few reluctant 8th graders left. After they're gone it's your program.